On a local level, weather may seem fickle: it may be rainy and windy one day and sunny and calm the next. But on a global scale, weather is not completely random: some places are almost always dry, some places always windy and other places always humid. We've learned to depend on these patterns: most people in northern North America own a snow shovel, and nobody living in the desert bothers with an umbrella. Earth's repeated weather patterns—its climate—shape the planet we know.
Wind and Weather
Global weather patterns are the result of the regular movements of air through the atmosphere.
Rising, warm, moist air creates a belt of heavy rainfall around Earth. Over land, this belt is home to most of the world's rainforests. Over ocean, weak winds led sailors to name this region the doldrums.
Descending, cool, dry air creates belts of little rain. These belts are home to most of the world's deserts.
Cold polar air collides with warmer air, creating a belt of stormy weather. High-speed, high-altitude jet streams, blowing from west to east, form at the boundaries between pockets of cold and warm air.
Rivers of Wind
About 12 kilometers (about 7.5 miles or 40,000 feet) up in the atmosphere, high-speed rivers of wind called jet streams circle the globe. Jet streams do not hold a rigid course—they meander back and forth, thereby changing weather patterns over weeks and months.
Where The Sun Shines
The Sun does not heat Earth evenly: around the equator, sunlight strikes Earth's surface more-or-less head-on. At the poles, the Sun's rays arrive at an angle and are far less intense when they reach the surface. And during certain times of the year, the poles receive no sunlight at all! As a result, the equator is hotter than the poles. Wind and ocean currents help even out planet's temperature differences by moving warm air and water from the equator to the poles.